This invention relates to a head clamp principally for use with radiological procedures and more particularly to a radiolucent head clamp having mechanisms for axially and rotationally adjusting the head-engaging pins of a head clamp, from a single side of the clamp.
An example of a head clamp with a single side control is shown in the Day, et al. U.S. Pat. No. 5,269,034, assigned to the same assignee as the present invention, discloses a head clamp having a generally C-shaped frame with a head-engaging pin on one side of the frame and a pair of rotationally adjustable head-engaging pins on an opposing side of the frame. The opposing side of the frame also contains a mechanism for first, adjusting the rotational angular position of the pair of head-engaging pins, and a second, translating or linearly moving the pair of pins with respect to the pin. While the above head clamp works well, it is constructed of nonradiolucent materials. Therefore, use of the above clamp may introduce undesirable artifacts in radiological images taken of a patient with the clamp attached.
Further, radiolucent materials are not well suited for certain components in the adjusting mechanisms of the above clamp design. For example, the head clamp disclosed in the Day, et al. '034 patent uses steel balls which move in and out of detents to move toothed gear rings into and out of engagement thereby respectively locking and unlocking the rotational mechanism. That construction requires very precise dimensional tolerances so that the motion created by the steel balls moving in and out of the detents consistently separates the toothed rings to disengage the teeth on the rings. If those components were made from a plastic-type radiolucent material, the clamping forces would, over time, cause the balls to deform and lose their circular shape. Further, the surfaces in contact with the balls would, over time, form tracks in the ball paths. Either or both of those conditions would eventually result in a loss of dimensional precision that over time would result in inconsistent and unsatisfactory clamp operation.
An example of a known radiolucent clamp is shown in the Day, et al. U.S. Pat. No. 5,276,927, issued to the assignee of the present invention discloses a radiolucent head support with a radiolucent skull clamp secured to the head support. The detailed construction of the head clamp is shown in FIG. 5 herein. Referring to FIG. 5, the radiolucent clamp has a single pin mounted on an adjusting screw 2 at a first end 1 of the clamp. A pair of head-engaging pins are mounted on a clevis 3 which is rotatably mounted in an opposite end 4 the of the head clamp. The clevis 3 is connected to one end of a shaft 5. The opposite end of the shaft contains threads 6 and a locking nut 7. A first toothed member 8 is connected to the clevis 3, and a second tooth member 9 is connected to the opposite end 4 of the head clamp. A compression spring 10 mounted on the shaft 5 between the toothed members 8,9 is used to apply a biasing force tending to separate the toothed members 8,9. In operation, the locking nut 7 is rotated on the threads 6 to move the locking nut 7 away from the opposite end 4 of the clamp. That permits the spring 10 to move the shaft 5 and clevis 3 to the left as illustrated in FIG. 5 thereby separating the toothed members 8,9 and permitting the clevis 3 to freely rotate. When the clevis is moved to its desired angular position, the locking nut 7 is rotated in the opposite direction thereby moving the shaft 5 and clevis 3 to the right as illustrated in FIG. 5 thereby engaging the toothed members 8,9 and locking the clevis 3 in the desired angular position. Thereafter, the adjusting screw 2 at the first end 1 of the clamp is rotated until the patient's head is secured in the clamp.
The above construction has several disadvantages. First, after the patient's head is secured in the clamp, it is difficult to change the angular position of the clevis 3 because the clamping forces applied by the adjusting screw 2 override the biasing force of the spring 10 that is used to separate the toothed members 8,9. Therefore, to change the angular position of the clevis 3, the adjusting screw 2 must be turned to loosen the clamp sufficiently that upon loosening the locking nut 7, the toothed members 8,9 are able to separate. The above mode of operation is less desirable than a design that permits the angular adjustment of the clevis 3 independent of the clamping screw 2. The prior art clamp of FIG. 5 presents a further inconvenience in the bulkiness of the first end 1 of the clamp. Further, applying the clamping force through the single pin on the clamping screw 2, results in less predictable and unequal reactive forces by the pair of pins on the clevis 3.